Make sure there is a hot-key or at least a menu item for everything you want to be able to do. It's cool you are in to it. I will try to help, but I wont have much time for another month still.
It will be tricky to do what I envision:
When a route is entered, it should zoom-out and show the entire route (just as it automatically does), but we would have to disable nemaGE/EarthBridge so the network update doesn't instantly zoom the map back in. From there you could return to GPS view, or play the route (if you don't know what I mean, type in an address, it will zoom out to show the route, scroll the left bar down and select "route:###", then press the play button to see Google Earth "fly" the route at any speed/height/angle configured in the preferences.)
We should also have buttons for "Search for nearest Chevron" and such since Google Local is built in. We would always have to set the "from" address based on the GPS icon.
I have one idea for the home screen graphic above... I would like to see that same thing but with a thin border around the sides and top. Then turn on the "overview-map" and make the border bend around it in the upper right too. ...or not ...it's just a thought
Buttons on the sides might work as a 2nd skin style, since you mainly want the map in front of you, but the wide-screen shows you a ton on either side.